Non-invasive Doppler sonography is widely accepted as a means of measuring blood velocity. However, in some situations, the volume flow rate of blood may be a better indicator of the state of disease. One potential application of volume flow measurements is the prediction of stenosis of both common and internal carotid arteries by monitoring common carotid blood flow. In principle, an adequate degree of stenosis (generally accepted as 50% diameter reduction), results in a measurably decreased volume flow. Investigators have attempted to quantify this volume flow reduction using different sonographic techniques, with varying degrees of success. Some authorities have suggested that the ratio of flows of the unaffected and stenotic carotid arteries is the best predictor of carotid stenosis. Volume flow measurements have also been suggested as a technique for short- and long-term follow-up of carotid endarterectomy.
Volume flow measurements may also be applied in the diagnosis and treatment of vascular malformations. Specifically, the measurement of volume flow may help to distinguish arteriovenous malformations and fistulae, which are high-flow lesions, from venous malformations, which are low-flow lesions. Moreover, volume flow measurements provide a quantitative way both of assessing blood steals and of evaluating the effectiveness of embolization therapy. Renal dialysis patients may also benefit from Doppler volume flow measurements. Either inadequate or excessive flow through angioaccess fistulae can have pernicious clinical consequences. Doppler sonography has been suggested as a way of quantifying this flow.
Several techniques have been developed to estimate blood volume flow from Doppler velocity measurements, each being characterized by certain advantages and disadvantages. Generally, in order to estimate the volume flow rate of blood through an artery, pulsed Doppler ultrasound is used to measure the velocity of the blood. From this velocity measurement, and a measurement of the diameter of the vessel, an estimate of the volume of blood flowing through the vessel may be made. This volume flow estimation technique assumes a parabolic blood velocity profile, and assumes a circular vessel. Other techniques, such as colour M-mode, directly measure the one-dimensional velocity profile, but still assume a circular artery. Still other techniques exist, (e.g. those using uniform insonation of a vessel), but are also prone to measurement uncertainties.
Thus, it is known in the art to approximate blood velocity measurements across an entire blood vessel lumen by using only a single-point velocity measurement from a conventional clinical ultrasound instrument at the centre of the vessel and assuming a parabolic velocity profile.
Previous attempts to measure blood flow from two-dimensional velocity profiles have proven to be inaccurate because of the difficulty in determining Doppler angle (see Akira Kitabatake "Quantitative Color Flow Imaging to Measure the Two-Dimensional Distribution of Blood Flow Velocity and the Flow Rate", Japanese Circulation Journal, Vol. 54 March 1990.)